1. Field of the Invention
The present invention relates to a color solid state image pick-up device, particularly with color mosiac filters arranged to correspond to each picture element of the solid state image sensor.
2. Description of the Prior Art
Generally, in such a color solid state image pick-up device, the method of obtaining a standard TV signal with only one solid state image sensor involves obtaining the desired color signal by correlatively processing the signals of adjacent picture elements. For example, it has been known to provide complementary color filters in a color resolving filter by comparing the output of the picture elements corresponding to the complementary color filter with those of the picture element of other color filters so as to obtain the original color signals of R(Red), B(Blue) and G(Green) or the color differential signals (R-G), (B-G) . . .
The color resolving filter for such a correlative process normally utilizes a construction in which the color filters are inversely arranged. That is, a number of kinds of color filters are arranged in a determined sequence along the horizontal scanning lines, while vertically, a color inverted in a determined correlation is arranged for each line. FIG. 1 shows an example of such an inverted filter arrangement.
Here, G identifies the green filter, R the red filter, B the blue filter, M the magenta filter and X the light shading part. The filters 1 in the first line are all G, those 2 in the second line are the repetition of R, M, B, X, those in the third line are all G, and those in the fourth line are the repetition of the B, X, R, M. Such a color mosiac filter is arranged so as to correspond to each picture element PE of the image pick-up part of a CCD (charge coupled device).
In this case as shown in FIG. 1, the filters 1 in the first line and filters 2 in the second line are respectively superposed on the upper half and the lower half of each picture element in IH (horizontal scanning line). In the same way filters 3 in the third line and filters 4 in the fourth line are respectively superposed on the upper half and the lower half of each picture element in the next scanning line. Similarly each picture element forming the horizontal scanning line has two kinds of color filters superposed over it. When the signal formed on each picture element is horizontally scanned, the color output signal shown in FIG. 2(a) can be obtained.
In FIG. 2(a), a clock leakage portion without an image signal occurs at the beginning and then the sum signal of the two picture elements is produced in the superposed state on the clock leakage component. The clock leakage signal is the noise signal produced by the influence of the transferred clock signal of the CCD upon the output amplifier of the CCD.
When the output of the solid state image sensor 11 is delayed 1H (1 horizontal scanning period) by a delay line, as is shown in FIG. 2(b) the clock leakage component is further added successively.
The signal on the second horizontal scanning line of the solid state image sensor, namely the signal of each picture element covered by the filters in the third and the fourth line is shown in FIG. 2(c). Then, the difference between the direct output signal (FIG. 2(c)) of the solid state image sensor and the 1H delayed signal (FIG. 2(b)) forms the differential signal as shown in FIG. 2(d). This is the difference between two adjacent horizontal scanning lines. When the clock leakage component of the direct output of the solid state image sensor and that of the output via the 1H delay element are largely different from each other, the differential signal also includes the clock leakage component as shown in FIG. 2(d).
By making use of the vertical correlation of the output of each picture element in this way, the luminance signal Y is obtained from the sum of the color outputs of two vertically adjacent horizontal scanning lines and the R-B signal and the M signal (corresponding to the R+B signal) is obtained from the differential signal as is shown in FIG. 2(d). By making use of the horizontal correlation in the line the R signal is obtained from the sum of R-B and M and the B signal from the difference. From the thus obtained signals Y, R and B for example a NTSC color signal can be obtained as the standard TV signal with the encoder (not shown in the drawing).
In the color solid state image pick-up device with the mosiac filter, the polarity of the R-B signal and that of the M signal are inverted every second clock period although R-B and M appear alternately from the differential signal 5 as is shown in FIG. 2(d). Hence, even if one tries to obtain R and B from R-B and M with the differential signal, the correct signals R, B cannot be obtained due to the above periodical polarity inversion.